Chronic pain is a major health concern affecting 80 million Americans at some time in their lives. Current pharmacotherapies are not effective long-term, which has led to the development and testing of gene therapy approaches. We and others have demonstrated that herpes simplex virus type 1 (HSV) based vectors can deliver highly effective pain-modulating transgenes to sensory neurons in vivo following inoculation of peripheral tissue. One major advantage of this approach is that painful tissue can be specifically targeted by local vector delivery. We believe that this advantage can be further extended by targeting specific neuron types responsible for chronic pain, thus enabling gene transfer to be tailored to specific types of pain, such as inflammatory or neuropathic pain, while simultaneously reducing deleterious side effects. We have recently shown that HSV-mediated transfer and long-term expression of the glycine receptor 11 subunit (GlyR11) can be used to control the timing and duration of afferent silencing with exogenous administration of glycine. Based on these findings and our recent success in the creation of highly efficient, fully retargeted HSV vectors, we hypothesize that we can selectively silence distinct subpopulations of primary afferents responsible for neuropathic and inflammatory pain, therefore providing injury specific pain relief. These studies will enable us to determine whether the same or different afferent populations underlie inflammatory and neuropathic pain and provide the rational basis for the future development of HSV-based gene transfer vectors designed to restrict analgesia to the relevant primary afferents. We anticipate that these studies will (i) provide a novel platform technology that will allow us to selectively express transgenes designed to modulate the function of sensory afferent subpopulations, a strategy that can be readily extended to other types of sensory nerve disorders;(ii) develop initial functional and physical maps of sensory afferent subtypes that upon silencing will block different persistent pain conditions, thereby providing essential information needed for targeted pain control;(iii) identify afferents that have been functionally altered to respond to painful stimuli providing further information on nerve fiber plasticity;and, (iv) identify potential risks associated with silencing of an inappropriate population of sensory neurons (e.g. altered proprioception). To achieve these goals, we have proposed a series of interrelated experiments described in 3 Specific Aims. In Aim 1, the infectivity of HSV vectors will be retargeted to selectively transduce (a) A2 fibers, (b) peptidergic and (c) nonpeptidergic C fibers. In Aim 2, we will complement transductional retargeting with transcriptional targeting using transgene promoters that will, when combined with transductional targeting, fine tune silencing specificity. The combination strategy is intended to create initial fine maps of subpopulations of sensory fibers within the larger transductionally targeted groups representing critical afferents for the response to different painful stimuli. In Aim 3, the retargeted HSV vectors will be introduced into the DRG by peripheral inoculation of animal models of inflammatory and neuropathic pain and the analgesic efficacy and side effect profiles will be established following glycine-induced GlyR11-mediated silencing. PUBLIC HEALTH RELEVANCE: Chronic pain is a major health concern affecting 80 million Americans at some time in their lives. Current treatments are not effective long-term, creating a substantial unmet medical need. Experiments described in this study are intended to develop insights into the role of specific nociceptor populations in chronic pain responses that may lead to methods to control pain by targeted delivery of a highly specific regulated pain silencing gene therapy.